Tesla Motors Inc. (NASDAQ:TSLA) chairman, CEO and co-founder Elon Musk defended the safety of the electric cars made by his company in a blog post, while revealing what was apparently responsible for a recently publicized Model S sedan fire.

According to Musk, a large, curved piece of metal that had fallen off a semi-trailer punctured the armor plate underneath the Model S, piercing the vehicle’s battery. “The geometry of the object caused a powerful lever action as it went under the car, punching upward and impaling the Model S with a peak force on the order of 25 tons,” Musk said in the blog post.

The Model S owner did not suffer any injuries, and the fire that broke out in the front battery module was contained by the electric vehicle’s built-in safety features, including internal firewalls and vents, Musk said. Firefighters punctured the top of the Model S lithium-ion battery, which led to the fire spreading before it was put out by a combination of water and dry chemical extinguisher.

Despite the fire, Musk claimed it is safer to power an automobile with a battery than with a tank of flammable liquid. “A typical gasoline car only has a thin metal sheet protecting the underbody, leaving it vulnerable to destruction of the fuel supply lines or fuel tank, which causes a pool of gasoline to form and often burn the entire car to the ground,” Musk said. Tesla’s CEO also provided some figures to back his claim, saying there is the equivalent of one vehicle fire for every 20 million miles driven in conventional vehicles, compared with one vehicle fire for every 100 million miles driven in Tesla vehicles.

The owner of the vehicle, identified as Robert Carlson, said in an email to Jerome Guillen, director of Tesla’s Model S Programs, that he remained a firm believer in the company and its vehicles. Carlson said in the email, reprinted with permission on the Tesla blog: “I guess you can test for everything, but some other celestial bullet comes along and challenges your design. I agree that the car performed very well under such an extreme test. The batteries went through a controlled burn which the internet images really exaggerates.”

After the news, and video, of the Model S fire surfaced, Tesla’s share price took a big hit. According to reports, Musk’s personal worth also took a hit, around $594 million, because of the falling share price.

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